WO-A-9842717 relates to the carbonylation of unsaturated compounds. In example 3 it describes the preparation of propanoic acid by reacting ethene with water in the presence of a catalyst comprising 0.1 mmol of palladium (II) acetate, 0.15 mmol of 1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl) propane and 0.2 mmol methyl sulphonic acid. Ethene was fully converted with 100% selectivity into propanoic acid at an average rate of 1500 mol/mol.hr.
WO-A-0172697 relates to the carbonylation of pentenenitrile to prepare cyanovaleric acid in the presence of a catalyst comprising a specific bidentate phosphine, arsine or stibine ligand. In this bidentate ligand the P, As or Sb atoms are connected via an organic bridging group and each substituted with two tertiary alkyl groups.
In the description a broad variety of possible bridging groups are mentioned. Although, in passing, divalent aryl groups, viz. dixylyl, are mentioned, preference is given to C3–C5 alkylene groups.
Furthermore a broad variety of possible tertiary alkyl groups are mentioned. In passing, it is mentioned that the tertiary alkyl groups include cyclic structures, viz. an alkyl substituted 2-phosphatricyclo [3.3.1.1{3,7}]decyl group. Preference, however, is given to bidentate diphosphines containing non-cyclic tertiary alkyl groups, such as tert.-butyl groups. These preferences are confirmed in the examples. The use of a catalyst comprising 1,3-bis (di-tert.-butylphosphino) propane as a ligand, viz. example 3 and 8, results in a higher reaction rate and conversion than the use of a catalyst comprising 1,2-bis (di-tert.-butylphosphinomethyl) benzene as a ligand, viz. example 9. Furthermore the use of a catalyst comprising 1,3-bis (di-tert-butylphosphino) propane as a ligand, viz. example 1, results in a higher reaction rate and conversion than the use of a catalyst comprising 1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl) propane as a ligand, viz. example 10.
WO-A-0185662 relates to a process for producing aldehydes by hydroformylation of a vinyl-group containing compound. The object of the invention was to obtain a high selectivity towards the normal product. The hydroformylation reaction is carried out in the presence of a catalyst comprising a group VIII metal and a diphosphine ligand containing two 2-phospha-tricyclo[3.3.1.1{3.7}]-decyl groups connected by a bridge X. A wide range of possible bridges are indicated by their generic formulae. However, only diphosphine ligands having a “ethane”, “propane” and “hexane” bridge are specifically mentioned. The examples disclose only the use of a catalyst containing rhodium dicarbonyl acetylacetonate and 1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl) propane.
In section 3.2 of his thesis “Phospha-adamantanes a new class of bulky alkyl phosphine ligands” (thesis submitted to the University of Bristol in April 2000), Robert Pugh describes the synthesis of 1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-o-xylene. No applications are indicated for this ligand.
Although the processes as described in WO-A-9842717 and WO-A-0172697 result in more than satisfactory reaction rates, there is still room for improvement. A process resulting in even higher reaction rates is therefore desirable.